rocks under the microscope. the rocks you need to know granite diorite gabbro dolerite basalt shelly...
TRANSCRIPT
![Page 1: ROCKS under the microscope. The ROCKS you need to know granite diorite gabbro dolerite basalt shelly limestone sandstone arkose greywacke marble schist](https://reader035.vdocument.in/reader035/viewer/2022070306/5515e894550346d46f8b502f/html5/thumbnails/1.jpg)
ROCKS
under the microscope
![Page 2: ROCKS under the microscope. The ROCKS you need to know granite diorite gabbro dolerite basalt shelly limestone sandstone arkose greywacke marble schist](https://reader035.vdocument.in/reader035/viewer/2022070306/5515e894550346d46f8b502f/html5/thumbnails/2.jpg)
The ROCKS you need to know
• granite• diorite• gabbro• dolerite• basalt• shelly limestone• sandstone• arkose• greywacke• marble• schist
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PPL XPL
Granite Note how light and clear it is under PPL and grey/white/black under XPL; main minerals – feldspars
(often microcline), quartz, biotite and muscovite
quartzquartz
muscovite
muscovite
biotitebiotite
plagioclaseplagioclase
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plagioclase
amphibole
amphibole
plagioclase
biotite biotite
PPL XPL
Diorite
Darker under PPL than granite with more coloured minerals; much plagioclase and amphibole/biotite, only small amount of quartz
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PPL XPL
Gabbro Coarse-grained; darker under PPL and brightly coloured under XPL; main minerals –
plagioclase, pyroxene and olivine
olivine
olivine
olivine
pyroxenepyroxene
plagioclaseplagioclase
![Page 6: ROCKS under the microscope. The ROCKS you need to know granite diorite gabbro dolerite basalt shelly limestone sandstone arkose greywacke marble schist](https://reader035.vdocument.in/reader035/viewer/2022070306/5515e894550346d46f8b502f/html5/thumbnails/6.jpg)
PPL XPL
Dolerite Medium-grained; darker under PPL and brightly coloured under XPL; main minerals – plagioclase
(often in form of laths), pyroxene (intergrown through other crystals) and olivine
plagioclase plagioclase
pyroxene
pyroxene
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PPL XPL
Basalt Fine-grained; darker under PPL and brightly coloured under XPL; main minerals – plagioclase,
pyroxene and olivine; often porphyritic (large well-formed crystals in fine groundmass)
pyroxenepyroxene
fine groundmass of
plagioclase & iron minerals
![Page 8: ROCKS under the microscope. The ROCKS you need to know granite diorite gabbro dolerite basalt shelly limestone sandstone arkose greywacke marble schist](https://reader035.vdocument.in/reader035/viewer/2022070306/5515e894550346d46f8b502f/html5/thumbnails/8.jpg)
calcite calcite
PPL XPL
Shelly limestone Dark under PPL and dark pearly shades under XPL; main mineral – calcite; note the
fossils.
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quartzquartz
PPL XPL
Sandstone Rounded quartz fragments; light under PPL and grey/white/black under XPL; main
mineral – quartz
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microcline
quartz quartz
microcline
PPL XPL
Arkose More angular quartz and feldspar fragments; light under PPL and grey/white/black under
XPL; main minerals – quartz and microcline
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quartzquartz
muddy
matrixmuddy
matrix
rock
fragment
rock
fragment
PPL XPL
Greywacke Fragments variable in shape, size and type; light under PPL and grey/white/black under XPL; main mineral – quartz but with rock fragments, feldspar and minor micas; look out for the muddy matrix!
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calcitecalcite
PPL XPL
Marble Crystalline with perfect cleavages evident; light under PPL and pearly shades under XPL;
main mineral – calcite.
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garnet
muscovite
quartz
PPL XPL
Schist Minerals showing foliation; light under PPL and brightly coloured under XPL; main
minerals – muscovite, biotite, garnet, quartz and feldspar
garnet
muscovite
quartz